source: http://www.securityfocus.com/bid/1908/info

ManTrap is a "honeypot" intrusion detection system designed to lure attackers into it for analysis. The honeypot is implemented as a chroot'ed Solaris environment, designed to look and feel real to an attacker who gains access to it. To ensure that the "lured" hacker doesn't realize that they are on a ManTrap host, certain processes must be hidden. One of the ways this is accomplished in ManTrap is through kernel modules that prevent /proc entries from being created for these processes. Unfortunately this is trivial to bypass through comparing process information retrieved directly from kernel memory to the contents of /proc.

The kill() system call does not read from /proc. A hacker may, for example, write a program to send SIGCONT (or another signal usually ignored) to incrementing process ID's verifying valid PIDs (that dont belong to them) by the errno value generated by kill() (EEPERM). The valid PIDs that are not in /proc would be the 'hidden' processes.


/*
 *  ManTrap detection/testing program by wilson / f8labs - www.f8labs.org
 */

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <strings.h>
#include <unistd.h>
#include <sys/signal.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <errno.h>
#include <dirent.h>

void check_proc_vs_kill(int listpids)
{ 
  struct stat st;
  int i, counter;
  char buf[520];
  
  printf("proc-vs-kill() test: \n");
  fflush(0);
  
  if (geteuid() == 0)
  {
    printf("  Error: Running as root. NOT performing /proc-vs-kill() test.\n");
    return;
  }

  if (listpids == 1)
  {
    printf("Listing mismatching PIDs:\n");
  }

  counter = 0;
  for (i = 1; i < 65535; i ++)
  {
    if ((kill(i, SIGCONT) != 0) && (errno == EPERM)) /* send SIGCONT (which hopefully won't matter) to the process */
    {
      snprintf(buf, 511, "/proc/%d", i);
      if (stat(buf, &st) != 0)
      {
        counter ++;
        if (listpids == 1)
        {
          printf("%.5d ", i);
          if (counter%8 == 0)
          {
            printf("\n");
          } 
        }
      }
    }
  }
  if (listpids == 1)
  {
    printf("\n");
  }
  if (counter == 0)
  {
    printf("  Normal: No mismatches found.\n");
  } else
  {
    printf("  ManTrap? %d mismatching PIDs found.\n", counter);
  }
}

void check_proc_dotdot()
{
  DIR *procDIR;
  struct dirent *procdirent;
  int found;
  
  printf("dotdot test:\n");
  procDIR = opendir("/proc");
  if (procDIR == NULL)
  {
    printf("  Error: Couldn't open /proc while performing dotdot test.\n");
    return;
  }
  found = 0;
  procdirent = readdir(procDIR);
  while (procdirent != NULL)
  {
    if (strcmp(procdirent->d_name, "..") == 0)
    {
      found = 1;
      break;
    }
    procdirent = readdir(procDIR);
  }
  closedir(procDIR);
  if (found == 0)
  {
    printf("  ManTrap? /proc/.. not found in directory listing!\n");
  } else {
    printf("  Normal: /proc/.. found in directory listing.\n");
  }

}

void check_proc_cwdwalk()
{
  char savedpwd[2048], newpwd[2048];
  
  printf("cwdwalk test:\n");
  if (getwd(savedpwd) == NULL)
  {
    printf("  Error: Couldn't get working directory while performing cwdwalk test.\n");
    return;
  }
  
  if (chdir("/proc/self") != 0)
  {
    printf("  Error: Couldn't chdir to /proc/self while performing cwdwalk test.\n");
    return;
  }
  if (chdir("cwd") != 0)
  {
    printf(" Error: Couldn't chdir to /proc/self/cwd while performing cwdwalk test.\n");
    return;
  }
  if (getwd(newpwd) == NULL)
  {
    printf("  ManTrap? getwd() failed after chdir to /proc/self/cwd.\n");
  } else {
    printf("  Normal: getwd() succeeded after chdir to /proc/self/cwd.\n");
  }
  chdir(savedpwd);
  return;
}

void usage(char *myname)
{
  printf("Usage: %s <-a|-p|-l|-d|-c|-h>\n", myname);
  printf(" -a performs ALL tests\n");
  printf(" -p performs /proc-vs-kill() test\n");
  printf(" -l performs /proc-vs-kill() test and lists mismatching PIDs\n");
  printf(" -d performs /proc/.. test\n");
  printf(" -c performs /proc/self/cwd test\n");
  printf(" -h shows this help\n");
}

int main(int argc, char *argv[])
{
  printf("ManTrap detection/testing program by wilson@f8labs.org - www.f8labs.org\n");
  if (argc != 2)
  {
    usage(argv[0]);
    exit(1);
  }
  if (strlen(argv[1]) != 2)
  {
    usage(argv[0]);
    exit(1);
  }
  switch(argv[1][1])
  {
    case 'a':
      check_proc_vs_kill(0);
      check_proc_dotdot();
      check_proc_cwdwalk();
      break;
    case 'p':
      check_proc_vs_kill(0);
      break;
    case 'l':
      check_proc_vs_kill(1);
      break;
    case 'd':
      check_proc_dotdot();
      break;
    case 'c':
      check_proc_cwdwalk();
      break;
    case 'h':
    default:
      usage(argv[0]);
      exit(1);
      break;    
  }
  printf("Finished.\n");
}
